Core B is designed to support oncoretroviral- and lentiviral-mediated gene transfer studies in Projects 1-5. These projects need to achieve efficient gene transfer into cells of hematopoietic origin, including dendritic cells and CD34+ hematopoietic cells. One clinical trial (in Project 5) also requires the production of a clinical grade retroviral vector. Thus, projects 1-5 require well-characterized and periodically tested high- titer producers cell lines and cell free retroviral stocks, as well as detection of replication-competent retroviral (RCR). The centralized generation of high-quality producer cell lines, retroviral stocks and biosafety testing is cost effective permits standardization of procedures, and facilitates the exchange of information and expertise between the five projects. In the pre-clinical phase of investigation, the specific aims of the RNA Core are: 1. construction of recombinant oncoretroviral or lentiviral vectors; 2. transfection of vector DNA in packaging cells and selection of producer cell lines; 3. characterization of vector transmission in standard cell lines; 4. expansion of independent clones and identification of the best clone for the intended target cells; 5. titration of cell-free viral stocks; 6. detection of replication-competent oncoretroviral in cell-free viral stocks and transduced target cells. In the clinical phase of investigation, the specific aims of the RNA Core are to carry out and/or coordinate: 1. the generation of high-titer producers, master cell banks and viral stocks for clinical studies; 2. the development of scaled up procedures for production of 5 to 15 liter batches of clinical viral stocks in semi-closed systems; 3. the development of a scaled procedure for the transduction of hematopoietic progenitor cells in semi-closed systems, in collaboration with investigators of projects 5; 4. The ability to carry out both production and transduction in the Gene Transfer and Cell Engineering Facility at MSKCC decreases the cost of generating materials and therefore the cost of clinical investigation. M. Sadelain, M.D., Ph.D., is the Director of Core B and I. Riviere, Ph.D, the Co-Director. Within the Gene Transfer and Cell Engineering Facility at MSKCC, they are currently assisted by two senior Research Assistants with considerable experience in cell culture, virology and molecular techniques and by Quality Assurance/Quality Control specialist who will review and assess all quality control issues related to the manufacturing and the release of the clinical vector and patient products.